1. Field of the Invention
The present invention relates to light communication equipment capable of communicating data with other equipment by light space communication.
2. Description of the Prior Art
With advancement of semiconductor technology, various small size and light weight portable terminal devices have been proposed in recent years. They include a device having a data communication function with other devices. A cable or an electric wave is used as a communication medium.
However, when the cable is used as the communication medium, the cost to install the cable is high and a significant restriction is imposed to movement, addition or removal of the device.
When radio transmission is used as the communication medium, there is no restriction on the movement, addition or removal of the equipment but the equipment is easily affected by an electromagnetically induced noise and it malfunctions in a plant where large machinery is operated. Interference to radio and television sets is unavoidable and subject to legal regulation.
Accordingly, light communication which radiates light such as infrared ray to a space to transmit data without using the above communication media has been investigated.
In the past, one-to-one communication has been primarily considered. In order to accurately align optical axes of a light emitting station and a light receiving station, a light emitting/receiving unit is separately housed from an information processing unit and the light emitting/receiving unit is fixed while the information processing unit is rendered movable to a certain extent.
There is no means for effectively determining whether the information processing unit is located within a range permitted for the light communication and such confirmation is made by actually transmitting data.
When a host computer and a terminal communicate with each other by light space communication, a terminal is installed within a light irradiation area of a light communication unit of the host computer which is located on a ceiling of a room and emits and receives light. A light communication unit of the terminal also receives and emits light.
Since the prior art light communication unit of a host computer uses a light emitting diode as a light emitting device, the light illumination angle is small and the light illumination area is small. Thus, the communication range is narrow. As a result, the movable range of the terminal is limited to a small area.
The prior art light communication is primarily intended for one-to-one communication and optical axes of the receiving station and the sending station must be accurately aligned. If one-to-one light communication is effected, a plurality of light from additional sending stations may reach the receiving station and cause interference.
In addition, power consumption in a light emitting unit for the light communication is large and hence it is difficult to provide portable equipment operated by a battery.
In order to effect the light space communication, the light receiving unit and the light emitting unit are necessary, and peripheral circuits are in many cases, discrete circuits. Therefore, there is a limit in reducing the size. Thus, if the light space communication unit is equipped with handy equipment, it is not possible to equip a unit for another function. If the processed data is to be printed out on record paper by a printer, the data should be transmitted to a large system having a printer by light communication.